The present application claims priority under 35 U.S.C. xc2xa7119 of German Patent Application No. 199 34 868.5, filed on Jul. 24, 1999, the disclosure of which is expressly incorporated by reference herein in its entirety.
1. Field of the Invention
The present invention relates to a heated drying cylinder for drying a fibrous material web partially wrapped around it, in particular, a paper, cardboard, or tissue web, in machines for producing and/or refining the same, in which a continuously circulating belt presses the fibrous material web against the cylinder jacket of the drying cylinder.
2. Discussion of Background Information
Such drying cylinders have been known for a long time, with the drying cylinders being arranged in one or more rows and the fibrous material web usually being guided around them in a meandering fashion. In this connection, one or more drying wires are often used as a supporting belt.
The drying cylinders, which are generally heated by steam, have a smooth surface for the purpose of guaranteeing a high heat transfer to the fibrous material web. However, this smooth surface is also associated with relatively large adhesive forces in relation to the fibrous material web, which causes problems upon removal of the fibrous material web after it has wrapped around the cylinder.
After the removal of the drying wire, the fibrous material web continues to adhere to the drying cylinder for a distance, albeit a short one. Only when the web tension is great enough does the fibrous material web detach from the drying cylinder and continue to follow the drying wire.
This can cause the fibrous material web to rip or at least to stretch with the risk of forming creases. The problem is amplified as machine speed increases.
An aspect of the present invention is therefore to develop a heated drying cylinder which, besides efficient drying, also allows for easy removal of the fibrous material web.
This aspect is attained, according to the invention, in that the cylinder jacket is air-permeable in the region of contact with the fibrous material web and the inner chamber of the drying cylinder is connected to a pressurized air source. A pressurized air cushion is formed thereby between the cylinder jacket and the fibrous material web such that an equilibrium occurs between the pressure of the pressurized air streaming from the drying cylinder and the contact pressure of the belt as well as the web tension. As a result, the removal of the fibrous material web is in fact assisted so that the fibrous material web can immediately follow the belt without stretching of the fibrous material web occurring. Furthermore, the heat can be transferred from the drying cylinder to the fibrous material web by means of the pressurized air.
The region of contact is defined as the region of the cylinder jacket that comes into contact with the fibrous material web during rotation of the drying cylinder. In order to prevent the escape of pressurized air in the region of the drying cylinder not wrapped around by the fibrous material web, fixed coverings can be arranged inside or outside the cylinder jacket.
The cylinder jacket should preferably be perforated in the entire region of contact with the fibrous material web. In order to even out the pressurized air cushion, it is further advantageous for the cylinder jacket to be wrapped at least in the region of contact by an air-permeable cylinder belt that is as smooth as possible; the cylinder belt should be embodied as a woven belt, preferably with metallic content.
Furthermore, the belt should be embodied as a drying wire in a known manner. In order to improve drying, it is advantageous for the pressurized air preferably to be heated in the drying cylinder.
Due to the lack of a contact surface between the drying cylinder and the fibrous material web, it is further advantageous for the cylinder jacket of the drying cylinder to be heated to a temperature of over about 200xc2x0 C., preferably in the range of about 200xc2x0 to 400xc2x0 C., which lies considerably above the generally common values. This can be accomplished with infrared radiators, gas burners, and/or induction heaters. This results in a greater drying output being achieved without damaging the fibrous material web as well as a stronger heating of the pressurized air on its way through the cylinder jacket. At these temperatures, water vapor is additionally guided from the fibrous material web to the pressurized air cushion, which has a positive effect on the drying performance.
In order to considerably facilitate a backside ventilation of the fibrous material web during removal but, on the other hand, also to guarantee a good heat transfer to the fibrous material web during the stable guidance thereof, the pressure of the pressurized air should be selected high enough that a pressurized air cushion forms between the cylinder jacket and the fibrous material web with a maximum thickness of about 2 mm, preferably between about 0.5 and 1 mm.
Because of the high efficiency, one or more drying cylinders should be used, in particular in the initial region of the drying section.
According to an aspect of the present, a drying cylinder for drying a fibrous web is presented, the cylinder including an inner chamber connected to a pressurized air source; and an outer cylinder jacket having an air-permeable region which is adapted to contact the fibrous material web.
According to another aspect of the present invention, the cylinder is used in machines for producing and refining at least one of paper, cardboard, and tissue web. In another aspect of the present invention, the circulating belt presses the fibrous web against said cylinder.
According to a further aspect of the present invention, the air-permeable region includes perforations. In another aspect of the present invention, a drying cylinder is presented having an air-permeable cylindrical belt, wherein the outer cylinder jacket is covered by the air-permeable cylinder belt, said the having a smooth surface arranged to contact the fibrous material web.
In another aspect of the present invention, the cylindrical belt is a woven belt. According to still a further aspect of the present invention, the circulating belt is a drying wire belt. Further aspects of the invention include providing pressurized air that is heated in the drying cylinder.
According to another aspect of the present invention, a drying cylinder is provided having a heating device arranged to heat said cylinder jacket to a temperature of over about 200xc2x0 C., in particular, in a range of about 200xc2x0 to 400xc2x0 C.
According to a further aspect of the present invention the heating device includes at least one of infrared radiators, gas burners, and induction heaters. According to still a further aspect of the invention the pressurized air is controlled to a pressure level which produces a pressurized air cushion between the cylinder jacket and the fibrous material web.
According to an aspect of the present invention, the pressurized air cushion has a maximum thickness of about 2 mm, and preferably between about 0.5 mm and 1 mm.
According to another aspect of the present invention, the cylinder jacket is metal. In another aspect of the present invention, the perforations are bores. According to a further aspect of the present invention, the air-permeable region is substantially the same width as the fibrous material web.
In another aspect of the present invention, the inner chamber includes a fixed cover positioned proximate a portion of the cylindrical jacket is not in contact with the fibrous material web, wherein the fixed cover is adapted to prevent pressurized air from escaping from the portion of the jacket which is not in contact with the fibrous material web.
According to a further aspect of the present invention, a drying section for drying a fibrous web, is provided having at least one drying cylinder having an inner chamber and an outer cylinder jacket having an air-permeable region; a circulating belt arranged to press the fibrous web against the outer cylinder jacket and belt being arranged to partially wrap around the at least one drying cylinder; and a pressurized air source connected to the inner chamber.
In another aspect of the present invention, the pressurized air source is adapted to form an air cushion between the outer cylinder jacket and the fibrous web. According to still a further aspect of the present invention, the drying section includes at least one of infrared radiators, gas burners, and induction heaters for heating said drying cylinder.
According to still a further aspect of the present invention, the cylinder jacket has an air-permeable region which is in contact with the fibrous material web. Further aspects of the invention include a cylinder jacket has perforations in said air permeable region.
According to other aspects of the present invention, the cylinder jacket is covered by an air-permeable cylinder belt, the belt having a smooth surface in the region of contact with the fibrous material web. According to another aspect of the present invention, the cylinder belt is a woven belt.
According to a further aspect of the present invention, the circulating belt is a drying wire belt. According to an aspect of the present invention, the pressurized air source is heated in the drying cylinder. In another aspect of the present invention, the drying section includes a heater positioned to heat said cylinder jacket to a temperature of over about 200xc2x0 C., preferably in a range of about 200xc2x0 to 400xc2x0 C.
In another aspect of the present invention, the pressurized air source is controlled to a pressure level which produces a pressurized air cushion between the cylinder jacket and the fibrous material web. According to still a further aspect of the present invention the pressurized air cushion has a maximum thickness of about 2 mm, preferably about 0.5 mm and 1 mm.
Further aspects of the invention include a cylinder jacket is metal. According to other aspects of the present invention the perforations are bores. According to another aspect of the present invention the air-permeable region is substantially the same width as the fibrous material web.
According to a still further aspect of the invention, the inner chamber includes a fixed cover positioned proximate a portion of the cylindrical jacket is not interface in contact with the fibrous material web, wherein the fixed cover is adapted to prevent pressurized air from escaping from the portion of the jacket which is not in contact with the fibrous material web.
According to an aspect of the present invention a process is provided for drying a fibrous web in an apparatus that includes at least one drying cylinder having an inner chamber and an outer cylinder jacket having an air permeable region, the process including: pressurizing the inner chamber of the at least one drying cylinder with air; and guiding the fibrous material web partially around the at least one drying cylinder with a circulating belt wherein the circulating belt presses the fibrous material web against the air permeable portion of the cylinder jacket.
In another aspect of the present invention, an air cushion is provided between said cylinder jacket and the fibrous material web. According to a further aspect of the present invention, the process further includes heating, through induction, the at least one drying cylinder with at least one of infrared radiators, gas burners, and induction heaters.
In another aspect of the present invention, the cylinder jacket has perforations in the air permeable region. According to still a further aspect of the present invention, the circulating belt includes an air-permeable cylinder belt, the belt having a smooth surface in the region of contact with the fibrous material web. Further aspects of the invention include a cylinder belt is a woven belt. According to other aspects of the present invention, the circulating belt is a drying wire belt.
According to another aspect of the present invention, the process further includes heating the pressurized air in said drying cylinder. According to a further aspect of the present invention, the cylinder jacket is heated to a temperature of over about 200xc2x0 C.; preferably in a range of about 200xc2x0 to 400xc2x0 C.
According to an aspect of the present invention, the process includes controlling the pressurized air to a pressure level which produces a pressurized air cushion between said cylinder jacket and said fibrous material web. According to another aspect of the present invention, the pressurized air cushion has a maximum thickness of about 2 mm; preferably between about 0.5 mm and 1 mm.
In another aspect of the present invention, the cylinder jacket is metal. According to a further aspect of the invention, the perforations are bores. In another aspect of the present invention, the air-permeable region is substantially the same width as the fibrous material web.
According to a further aspect of the present, the inner chamber includes a fixed cover positioned proximate a portion of the cylindrical jacket is not in contact with the fibrous material web, wherein the fixed cover prevents pressurized air from escaping from the portion of the jacket which is not in contact with the fibrous material web.
Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure and the accompanying drawing.